BS IEC 61505:1998 pdf download – Nuclear reactorinstrumentation——Boiling water reactors(BWR)— Stability monitoring

BS IEC 61505:1998 pdf download – Nuclear reactorinstrumentation——Boiling water reactors(BWR)— Stability monitoring.
Thermal hydraulic instability is a known phenomenon in conventional steam generators. Two phase flow oscillations in steam generators can result in local rhannel overheating. This phenomenon and its impact on the design of steam generators is well documeiited tinder certain conditions boiling water reactors are also suseeptihit’ to auth thermal hydraulic intabilities. The design of the reactor rocirculation system has a large impact on the stability o(the reactor system. Four different BWR rt’circulation systems are used in modern BWHs:
it) Internal pumps (Figure Ia)
b) Jet pumps (Figure Ib)
c) lxternaI pUtItIi&4 (Figure Ic)
d) Natural recirculation (Figure id) Another critical factor in BWR stability is the neutronic feedback to the bwnl fuel channel thermal-hydraulic perturbation. ‘flie two feedback mechanisms. thcrmal.hydriiulic and neutronie. tire coupled in a KWH core and can, under certain citnditiciiis, gt-iierae scillatiigis 11 both cure flow and thermal power. In addition, reactor rnstabilities can occur even when neither feedback mechanism alone is sufficient to generate instability. The physics of such BWH.instabiliLies are explained with some detail in clause 5.
In order to identify flux oscillations characteristic of it thermal-hydraulic instability, a system that, monitors neutron flux (Al-’l(M and LPH!t signals) can be used This system generates an output signal which can be used for automatic suppression functions. A short description of automatic detection and suppression is included in Annex A.
A short account of examples of KWH instability incidents which have occurred during the last several years ta given in Annex B. These events illustrate the imp..irt.an€-c and the need for a standard on stability monitoring of IIWU. A significant amount iii information is now nvailabh’ relative to BWR stability from experience at operating BVRs. Special tests have been perfia-im’d at numerous plants under controlled conditions to provide information on individual plant response during an instability and the portion of the operating domain most susceptible to oscillations for the operating cundit ions present at the time of the test. Examples of such special tests are given in Annex C
An instability prevention concept is described by the power (low diagram given in Annex I). which is used in Japan and Germany.
In Annex E an account experience with stability monitoring in different countries is given. Annex F gives an estimation of neutron noise chnriictcristic functions, while the estimation of phase difference is described in Annex 0. Annex H is a luliliography.
1 Scope and object
This International Standard applies to boiling water reactors (HWR) designed to ensure that thermal-hydraulic osrillat ions are either not possible, or can be reliably and readily detected and suppressed, Compliance with the criteria can he demonstrated by:
a) preventing power oscillations:
b) detecting and automatically suppressing power oscillations.
Monitoring of the reactor stability state, which is the object of this standard, can support a) and b) by providing information on phint stability characteristics. Monitoring will detect the approach to, and oscillations.
The purpose of this standard is to
— describe appropriate plont parameters for Use
in stability monitoring:
— define analysis methods for relating
time-varying plant information to reactor
stability figures of merit, such as the decay ratio:
provide technical guideliuies regarding stability monitoring functional and performance requiri•mu’ntuu.
The following items are not covered by this standard:
a) control system instability:
b) recommendations for implementing a pnrticular solution or a combinnt ion of solutions:
c) requirements for analytical methods associated with each methoul;
d) requirements for manual operator and automatic act-ions necessary to suppress priwer oscillations or reduce decay ratios:
e) general safety significance of reactor instability,
This standard also does not cover predictor type stability monitors (e.g. frequency dumuin models which may be used on line to calculate decay ratio for current reactor conditions).